It is a familiar practice to also use roller curtains made from laths for sun protection. For this purpose, a user will let down the roller curtain a bit, so that the roller curtain casts an appropriate shadow. Relatively little light gets through the roller curtain itself. The ratio of slots to the overall surface is about 1.5%. As a result, the roller curtain generally cannot be let down entirely for sun protection purposes since the resulting darkness would be too deep.
Known roller curtains are made from individual laths with a bottom with an undercut channel and a hooked slat at the top. Extremely tiny slots, relative to the surface of the roller curtain, are situated in the area of the hooked slat. Thus, larger slots cannot be provided on the main body of the lath since it no longer would be possible to control the admission of light by rolling the roller curtain up or down.
Known laths have a roll shaped profile that is often packed with foam or provided with crosspieces running in the longitudinal direction of the lath in order to achieve the necessary strength.